boyle



June 27, 1939. J, BOYLE Re. 21,127

AIR VELOCITY METER Original Filed Dec. 23, 1933 3 Sheets-Sheet l June27, 1939. J, R, BOYL: Re. 21,127

AIR VELOCITY METER I Original Fil ed Dec. 25, 1953 3 Sheets-Sheet 2 J nT M' MM June 27, 1939.

J. R. BOYLE AIR VELOCITY METER 5 Sheets-Sheet 5 Original F'iled Dec. 23,1953 imQshock will not injure these .Reiesued June 27, 1939 Joann.'Boylefc'hicago, 111., assignor .tolllinoia I Testing Laboratories,Inc., Chioagm'IlL, a corporation in Illinois Original No. z,oao,s4s,dated November 17, 193s, Serial No. 703,753, December-'23, 1933.Application for 149,918

3'! Claims. (Cl. 73-4802) The present, invention relates to an airvelocity meter. Y i

One of the principal objects of the invention is to provide an, improvedconstruction of small,-

5 compact, portable meter which can be conven iently carried from placeto place for measur-.

ing air velocities. In this regard, it is a further object of theinvention to provide an improved I meter which is constructed andbalanced for accurate operation in any plane, 1. e.,' it can be held orsetvertically, horizontally, or at any interinediate angular positionfor measuring the velocity of an air stream flowing in any direction.This feature is of decided advantage for ll enabling one to determineaccurately the angle or direction of a low velocity air flow by merelycomparing readings with theinstrument held at di fl'erent angles. 3

Another object of the invention is to provide .1 an improvedconstruction of .meter of extreme sensitivity, capable of accuratelymeasuring air currents of very low velocities. For example, meters whichI have heretofore constructed embodying my invention are capable ofaccurately measgg uring such ve'ry feeble air currents as may be inducedin the free air of a room by heated air rising from a radiator, or asmay be set up by window ventilation or byconditioned. air circulatedthrough the room by air conditioning, ducts. Thus, my improved meterisof-marked utility for heatingand ventilating engineers, in that itenables accurate determination to be made of ,the direction and velocityof air currents in different parts of a room or otherenclosure, and ggto determine the velocities of air currents passing through inlet orexhaust ducts associated with an air conditioning system, etc.

, ,Another'object of the invention is to provide ,a meterof the abovecliaracteristics which is 4o also rugged and durable so that it canwithstand without injury the most severe shocks and jars to which aportable instrument is ordinarily subjected. Inthis regard, it is anobject Oftheinvention' to provide improved. means which is operativewhen the meter is not in use to imposea locking'force on the movingsystem so as to prevent movement thereof, and which is also 5perative torelieve relatively delicate bearings of the load ,of the moving systemso that jar or bearings or other parts. The efllcacy of this improvedconstruction has been demonstrated by meters 'constructed in accordancewith mydnvention which have been dropped from the height of a tablewithout g -in;|u ry; I

reissue June 23, 1937, Serial No.

My improved meter is preferably constructed as a direct readinginstrument calibrated to indicate directly the air velocity in feet perminute, and it is another object of the invention to provide improveddamping means which will prevent objec- 5 tionable oscillation orfluttering of the indicating pointer when reading rapidly pulsating aircurrents. The prior direct reading meters with which I am familiar haveutilized air'vanes and other like damping devices-but these damping indevices do. not prevent the aforesaid objectionable oscillation of theindicator, which oscillation may be so wide and rapid under someconditions as to make the reading of the instrument impossible. This hasbeen completely avoided 16 in my improved construction by employingimproved magnetic damping means. which results in the meter givingsubstantially a dead beat in-- .dication even when operating under themost adverse conditions. In my improved meters embodying this magneticdamping means, the inan improved construction which will enable the theair or gas velocity within a closed duct or pipe. This attachmentapparatus comprises tubes whch can be inserted through a hole in theside of the ma air or gas duct, and which tubes communicate at theirother ends witiithe meter.

1 Thus, the instrument may be readily converted into a flow meteradapted for measuring the velocity' of an air or gas within a closedconduit through the instrument-silty of Pitot tubes or the like. In thisregard, while most of the aforementioned features of my invention'havegreatest utility in a portable'air velocity meter such as I havedescribed, nevertheless it will be underinstrument;

stood that some of these features can be embodied with advantage instationary flow meters and other like instruments for'measuring thevolume or velocity of a fluid flow. Accordingly, my invention is not tobe limited in its entirety to a portable, air velocity meter.

Other objects and advantages of my invention will appear from thefollowing detail description of a preferred embodiment thereof. In theaccompanying drawings illustrating such embodiment:-

Figure 1 is a front elevational view of theimproved instrument;

Figure 2'is a side elevational view, illustrating the side through whichthe air stream enters the Figure 3 is a similar view of the oppositeside, illustrating the side from which the air stream is discharged fromthe instrument;

Figure 4 is the front view with the front cover removed, and some of theparts illustrated in section; a

Figure 5 is a transverse sectional view taken approximately on the planeof the line 5-5 of Figure 4 and looking in the direction indicated bythe arrows; I

, Figure 6 is a view taken approximately on the same plane, but lookingin the opposite direction, as indicated by the arrows 5-6;

Figure 7 is a perspective view looking at the open front of theinstrument, but with the plate which defines the bottom and front sideof the air channel removed;

Figure 8 is a perspective view of this plate;

Figure 9 is a detail sectional view of one of the improved bearings forthe moving system;

Figure 10 is a diagrammatic view illustrating the use of the instrumentfor measuring the velocity of unconfined or ambient air;

Figure 11 is a similar view illustrating the use of the instrumentfor-measuring the velocity of an 'air stream issuing from a duct;

Figure 1 2 is a diagrammatic view illustrating the use of the instrumentfor measuring the velocity of an air or gas flow through a duct;

' Figure 13 is a fragmentary sectional view showing one arrangement bywhich my improved meframe and having its ends secured to ether as in-.

dicated at 24. The front and back coverplates 2| and 22 have grooves25and 26 formed around their inner edges for receiving the edge portionsof the sheet metal strip 23. A. block 21, serving primarily for mountingor attachment purposes,

is extended across the upper portion of the housi 18, substantially fromside to side thereof, this lock being of lessendepth than the depth ofthe casing, as illustrated in Figures 5 and 6. This block is securedfast against the back cover plate 22, the cover plateand block beingfastened together by the 23 (Figs. 5 and 6). The

' front cover plate 2l'is detachably secured in place by .screws 23,which pass through the upper corcover plate are connected by screws 3|extending through both plates and receiving nuts 32 on their rear ends.It will be understood that the housing can be constructed in other waysthan that above described. For example, the back 22, the peripheralportion 23 and the mounting block portion 21 may be molded as a unitarypiece, omposed of a phenolic condensation produ t, or aluminum or anyother preferred material.

Defined below the block 21 is the air channel or passageway 34 in whichthe air vane 35 oscillates in response to the velocity of the airpassing through said channel. the channel passes through upper and lowerapertures 36, 36' provided in the lefthand vertical side 231 of thesheet metal frame structure 23. The air leaving the channel orpassageway 34 passes out through a somewhat similar arrangement ofapertures 31, 31', 31" provided in the righthand wall 231' of this sheetmetal casing portion 23. As I shall hereinafter describe, shutters arepreferably associated with these difierent sets The air entering ofholes for restricting one of the sets and for ing its righthand endfixedly secured to the attachment block 21, as by having the end of thisstrip bent upwardly and secured to the top .of-

the block around the end thereof; or such attachment may be effected inany other desired manner. The other end of thesheet metal strip 38 isarranged so that it canfbe adjusted upwardly or downwardly to vary thesize and shape of the air channel 34. This adjustment is effected by ascrew ll which passes down through the mounting block 21 and has itslower end threading through a threaded bushing 42 which is suitablyanchored to the top side of the strip 38; The left extremity of thestrip 33 is left free so that it can move up and down in the adjustmentseffected by the screw ll. The head of the screw II is accessible throughan" aperture 43 in the top wall 23f of the sheet metal housing portion.This hole 43 may be smaller than the head of the screw ll "so as to holdthe screw against upward movement, the screw being mounted in the block21 before said blockis enclosed within the perimetrical housing portion23. If desired, a compression spring 4| may encircle the screw and thethreaded bushing 42, such spring thrusting the strip 38 downwardly tothe adjusted position established by the screw 4 I The air vane 35swings about the axis of a pintle-or arbor 45, the are 46 designatingthe path of movement of the upper edge of said vane. When the vane is inits zero position, it lies substantially in the full line positionillustrated in Fig. 4. Directly above the arc-l6,-the under side of thesheet metal strip 38 is formed with a curvature 41 extendingsubstantially from thisvzero'position of the vane to the righthandextremity of the air channel 34. The curve 41 may be a'true are or maybe a parab-' ola or other generated curve, depending principally on themanner in which it is desired to subdivide the indicating scale on theinstrument.

With the scale graduated as shown in Figure 1, I

preferably form the curve 41 as a true arc. The

relation betweenthearc 46 of the vane and the curve 41 issuch that anaperture a is constantly defined between thesecurves, this aperturebeing position, and constantly increasing in. height and size as the.vane swings towards its position of I of minimum height'when the vaneis in'its zero maximum air velocity. The adjustment afforded by thescrew 4i enables the size of the aperture a to be increased or decreasedwith the vane disposed in its zero position. Such adjustment also 5enables the height and shape of the curve 41 to be varied for securingscale corrections.

The bottom of the air channel or passageway 34 is defined by a plate 49,illustrated in per-, spective in Figure 8. This plate comprises avertical front portion, 49a from which the bottom wall portions 49b and49care bent rearwardly. Attaching flanges 49d are bent downwardly fromthe rear edges of the bottom wall portions 491), 48c. Screws or othersuitable fastening members 5| 5 pass through apertures in these'fianges49d and engage in the back coverplate 22.

front portion 49a is provided with apertures 48c for receiving screws 52which fasten in the at: tachment block 21. An aperture 49! is providedbetween the bottom wall portions 491) and 490,

and the vane 35 extends upwardly through this. aperture. The lowerportion of the vane is formed with a cylindrically curved portion 35awhich is arranged just out'of-contact with the inner-edge 49g of thebottom wall portion 49b.

The very narrow slot affording mechanical clearance between this edgeandthe curved portion, 35a remains of the same size throughout theentire throw of the vane so that the leakage around the under side ofthe vane at this point is maintained at a constant throughout the entiremovement of the vane. The slope of the bottom wall portions 4% and 49c,substantially as shown, accommodates a greater range of movement of thevane and affords other advan:

tages. The front wall of the air channel 34 is defined by the verticalfront portion 49a. of the plate 49, and the back wall of the air channelis defined by the rear cover plate 22, the front and rear edges of thevane being spaced slightly from,

these walls, as illustrated in Figure 6.

Mounted horizontally in the lower portion of the casing is a U-shapedpermanent magnet 54.

The mounting of said magnet is preferably established through a bracket55 (Figure 6) which is secured to the back cover plate 22 ,by screws5.6.

The bracket 55 'is secured to the side of the magnet by lugs, screws orsoldering. In the preferred embodiment shown, the moving system of themeter is mounted on the magnet-54 and bracket 55, although it will beunderstood that difierent arrangements of mounting brackets may beemployed. The moving sys em comprises the vane 35, vcurved lower portion35a, spindle 45 55 and damping segment 58. The lower end of the curvedportion 35a is formed withan inwardly extending tongue portion 8517which is crimped around the spindle 45 or otherwise fixedly securedthereto. The dampingsegment 56 is dis- 30 posed to swing between theclosely disposed pole extremities of the magnet 54,as best showninFigure 7. This segment has an upwardly extending tongue portion 58awhich is apertured for 75 made of other materials, if desired.

The vertical .front leg of the magnet 54.

spindle .on said boss.

1 provided in the front cover plate'2l.

permitting the spindle 46 to pass therethrough.

The opposite ends of the spindle 45 are formed with pointed extremities45a, as illustrated in the enlarged section of Figure 9 Theseextremities ,extend into tapered sockets 6| formed within jewel bearings62 which are mounted within the 5 bearing bushings 63. In the preferredconstruction of these bearings, the socket 6| is formed on Y a moregradual taper than the spindle extremity 45a so that the bearing contactoccurs primarily at the larger end of the socket, substantially at 10the point indicated at Gla. This portion of the. 1 socket is slightlylarger than the adjacent portion of the spindle extremity so that the,spindle can be moved upwardly to contact with the top portion of. thesocket 6| when the weight of the 15 moving system is taken oil of thebearings. The bearing construction is the same at both ends of thespindle The rear bearing bushing 53 screws through a bracket 64 which isattached either to the mounting bracket 55 or to the upper 20 edge ofthe magnet 54 .(see Fig. 7). Thefront bearing bushing 63 screws througha front bearing bracket 65which is suitably fastened to the Referringagain to Figure 9, a lock nut 66 screws over the outer 25- 7 end of thebearing bushing 63 and abuts against the outer side of the bracket 65."This lock nut has an annular shoulder or boss 66a projecting inwardlytherefrom. Said shoulder or boss defines an annular bearing for an arm61 (Figurefi) 30 which is pivoted to oscillate about the axis of the-The swinging end of this arm is provided with aninwardly projecting ex-,tre'mity 61a, and to this extremity is suitably J fastened the outerend of the hairspring 68; The 35 inner end of the hair spring issuitably secured to the spindle 45. The hair spring is preferablyarranged as shown in Figure 4, whereby the convolutions of the spiralare wound up as the vane 35 swingsto the right, although thisarrangement '40 of the hair spring is not essential. The tension of lthe hair spring can be increased or diminished for thepurpose ofaccurately setting the pointer on its zero position, by the rotation ofa small screw II which has threaded mounting in the 45 frontcover plate2|, and the front of which screw is accessible from the front of theinstrument. The rear end of this screw has an L'- shaped arm I! securedthereto (Figure 6), and

the inwardly projecting end of thisarm or lever =50 extends through anaperture in the armli'l, whereby rotation of the screw 11 is operativeto oscillate the arm 61 and thereby increase or decrease the tension onthespring 68. 7

The dial is printed one. card ,or plate 14, which 55 is suitably securedto the front side of the vertical wall portion 49a of the plate 49. Thedial markings are visible through asight window 15 A glass 161s mountedin this sight window l5.' The pointer 11 consists of a rod or wire whichis Secured j to the movable system in any suitable manner,

preferably by, bending a portion of the rod'in' wardly belowtheverticalwall 49a, the'nepassin'g the rod downwardly through anaperture in the 05 curved vane extension 35a and through an' aperture inthe spindle 45, and th n bending the extremity of the' rod inwardly seatin g notch in the'lower portion of the damping segment extension No, asshown in Figures 6 and 4-. 'm

Devices are provided for adjusting the balance -or center of mass of themoving system in two different directions. Referring to Figures! and '7,one of these devices consists of a small angleshaped clip or arm llwhich is pivoted at- 19 to 15 to this flange 58c, said latter balancingdevice being capable of pivotal adjustment in a plane defined by the topsurface of the flange 58c and affording center of gravity adjustment inanother line of direction. By shifting the position of one of these twoadjustable balancing members the center of gravity of the moving systemcan be shifted in one direction, as for instance vertically towards oraway from the horizontal plane of the pivot axis; and by shifting theposition of the other balancing member the center of gravity can beshifted in another direction, as for instance horizontally towards oraway from the vertical plane of the pivot axis. Convenient access may behad to these adjustable balancing members 18 and 8| by merely removingthe front cover plate 2i. p

The concentrated flux field of the magnet 54 is primarily in the narrowgap 54g defined between the closely disposeed pole extremities 54a ofthe magnet. Referring to Figure 4, I have found it preferable to shapeand arrange theadjacent edge of the damping segment 58 substantially asshown, with the diagonal edge 58c 01' the segment intersecting a limitedportion of this concentrated flux field when the pointer 11 is'in itszero position. Certain advantages accrue to this formation of theadjacent edge of the damping segment and to this relation of the segmentto the concentrated flux field. For instance, the restoring forces whichare necessarily exerted by the balance of the-moving system and by thetension of the hair spring, for the purpose of returningthe pointer tozero position, can be reduced to a minimum or can be made practical- 1ynil when the pointer arrives in its zero position,

because the magnetic damping action is exerting very little motionretarding force substantially at the time that the pointer isapproaching or arriving at its zero position. on the other hand, as soonas the vane 85 starts its oscillation to the right in response to acurrent of air, the damping action becomes increasingly effective asthe. diagonal edge 58e oi the damping segment swings upwardly throughthe concentrated ilux field, whereby a maximum damping actioniseffec'tive at the higher air velocities.

The device for imposing a locking and elevating force on the movingsystem when the meter is not' in use comprises a, resilient wire 88which has a U-shaped resilient loop 880 at one end. as shown in Figure4. The front bearing bracket 88 has an extension portion 88a projectingdownwardly on the inner side of the magnet '88, and the upper end'of theloop 88:; is soldered or otherwise suitably secured to the lower-end ofthis extension-portion 88a. The wire is bent to have a rearwardlyextending portion 88b passing below the circular outer periphery of thedamp ing' segment l8 (Figure 8). and this portionot the wire has aU-shaped bend 88c therein for engaging the peripheral edge of thesegment. The wire continues diagonally upwardly andto theAnotherbalancing device 8| of 86. When the latter shutter is in eitherof its open positions for permitting the passage of air through thechannel ll, the wire is pressed downwardly to remove'all restraint fromthe damping segment 58, but when the shutter is moved upwardly to itsclosed position, the wire is carried.

upwardly thereby to impose an upward force against the bottom edge ofthe damping segment, thereby locking the moving system against motionand also lifting the moving system so that the weight thereof is notcarried by the tapered spindle ends 45aand bearing jewels 82. When themoving system :is thus locked against motion, and its weight removedfrom the bearings, it is capable of withstanding very severe jars.

The shutter which controls the inlet apertures 38, 36' comprises a plate85 which is arranged for vertical sliding movement along the inner sideof the lefthand housing wall 231. The plate has laterally bentstiffening flanges 85a along its vertical margins. ISuitable provisionis made for guiding the plate for vertical sliding movement, whichguiding arrangement may be of any desired form, although in thepreferred construction. shown I have illustrated resilient rods or wires88 which have their upper ends anchored.

in the mounting block 21 (Figure and which have their lower endspressing frictionally against the inner surface of the plate at pointsjust inside of the marginal stiffening flanges 85a, where the rods serveto guide the vertical motion of the plate. Referring to Figure 4, saidrods are formed with hump-shaped or rounded lower ends 86a which areadapted to snap into slots 85b in the p the lower portion of the shutterplate.

shutter plate 85. The plate is reciprocated by the rotation of a thumbwheel 81 which is mcunted at the lefthand side of the instrument. Ashaft 88 projects from this wheel through the housing wall 281 and has arod 89 anchored to its inner end and projecting rearwardly therefrom.Said rod extends through an aperture 850 which is provided in a flange85d projecting from Rotation of the thumb wheel 81 is thus operative toreciptop of this recess ll.

- left, as indicated stud: for attachment to the shutter which controlsthe, leithsnd apertures-88.

ro'cate the shutter plate upwardly or downwardly. The downward motionthereof is limited by the lower diagonal edge 85s of the plate engagingthe thumb wheel-shaft 88. The upper edge of the plate is adapted toslide up into a recess 9| between the attachment block 21 and casingwall 28!, and the upward motion of the plate is limitedby the engagementof said plate with the Provided in the plate 85 is a row of relativelylarge apertures 92, as large as the apertures 88, 88' in the casingwall, and upper and lower rows of'relatively small apertures 88 and 88'.The apertures in the shutter plate and in the casing wall are so relatedthat when the shutter plate is in the lowermost position as illustratedin Figure 5, the top' edge of the plate is below the'upper row of easingapertures 38 and the row of shutter apertures 82 is in'registration withthe lower row of easing apertures 38. This leaves the casing aperturesentirely unobstructedgfor a maximum flow of air therethrough.

, Whentiie shutter plate is moved upwardly to its intermediate position,as determined by the action of the detent humps 88a snapping into theintermediate apertures 85b, the top row of 1 small shutter apertures isbrought into registration with the top row of casing apertures 36 andthe bottom row of shutter apertures 93' is brought into registrationwith the bottom row of casing apertures 38'. This reduces the totaleffective area of the openings through which the air can enter theinstrument, such area bearing a predetermined relation to the totaleffective area of the casing apertures 36, 36' when unrestricted,whereby the instrument can be used to measure air velocities which wouldexceed the capacity of the instrument if the air flow were through theunrestricted casing apertures 36, 36'.

When the shutter plate is raisedto its uppermost position, the solidportion of the plate directly below the top row of small apertures 93closes 58 and thereby lift and lock the moving system to place themoving system in inoperative condition as well. This is accomplished byextending the end 83d of the lifting spring into an aperture in thelower portion of the shutter plate 85, as

shown in Figure 5, whereby the lifting spring is caused to move upwardlyagainst the peripheral edge of the damping segment when the shutterslide is in its uppermost position.

The dial 14 is provided with two concentric scales Stand 95, so arrangedthat the pointer 'ii swings over both scales. The inner "scale 94 isshown as being calibrated to read from 0 to 400 feet per minute, and isthe scale which is read when the inlet apertures 36, 36' are openedwide, corresponding to relatively feeble air currents. The outer scale95 is calibrated to read from approximately 0 to 2500 feet per minute,

and is the scale which is read when the air enters through therestricted apertures 93, 93', corresponding to relatively high airvelocities. tongue 85 is bent laterally from the forward edge of theshutter plate 85 in position to extend over the front of the dial ll,this tongue moving up and down with the shutter plate and serving as anindicator for designating whether the inner scale 94 or the outer scale85 is to be read. It will be apparent that the indicator is in positionv to designate the inner scale 84 when the apertures 36, 36' areunrestricted, and will be in position to designate the outer scale 95when the air flow is through the restricted apertures 93, 93".

Figure diagrammatically illustrates the use of the meter for measuringthe velocity of an unconfined air flow, such as the circulation of airin a room or enclosure. By reason of the straight through flow of theair in the instrument-its entrance through the inlet apertures 36, 36'at one side of the casing, its substantially straight line flow throughthe channel 34, and its discharge through the outlet apertures 81, 31',31" at the oppositeside of the casingthe' instrument is made moreemcient and more sensitive and can be used to'better advantage fordetermining accurately the direction of an unconfined air flow by merelytilting or turning the instrument to difierent'angular positions andnoting any variation in the readings. The substantially straight I inFigure 13,

line flow of the air through the instrument, as distinguished from asinuous, tortuous or reversing path,'greatly reduces the inertia lossesand side wall air friction. By minimizing these losses,

and particularly the inertia losses, the maximum kinetic energy of veryfeeble air currents is imparted to the vane. It will be noted fromFigure 6; that the vane closes almost the entire rosssectional area ofthe channel when in its ero position, there-being only small clearanceareas betweenthe channel walls and'the side and top edges of the vane.It will also be noted from Figure 4 that in all positions of the vane itcloses the major cross-sectional area of the channel. These factorsgreatly increase the sensitivity and accuracy of the instrument to lowvelocity air flows.

Figure 11 diagrammatically illustrates the use of the instrument fordetermining the velocity of an air current issuing from a duct D. Ineach of the uses illustrated in Figures 10 and 11, the out? letordischarge apertures 31-41" at the outlet side of the casing ,aremaintained open. For

obtaining an average of the velocities issuing from the diil'erent radiiof such a duct D, it is customary to take readings while moving themeter laterally across the end of the duct. This transverse movement ofthe meter in a direction perpendicular to the direction of air flowdoesnot disturb the accuracy of the readings because of the fact that theinlet and outlet openings 36-35 and 31-31" are in opposite side walls ofthe meter casing, and hence any effect which such lateral or transversemovement of the casing may have on one opening is counterbalanced by thesimilar effect on the other opening. a

.;Figure 12 diagrammatically illustrates the use of a modified form ofmy improved meter for measuring the velocity of an air or gas flowoccurring within a closed duct D. or other region of air flow removedfrom the-meter casing. In adapting the meter to this utility, anattachment 91 is connected with the meter for conducting the air or gasfrom the duct D throughthe meter and back into the duct. This attachmentcomprises two pipes 98 and 99 having apertures 98' and 99' in their,upper ends. The apertures 98'- are arranged to face in opposition to thedirection of the flow and the apertures 99 are arrangedto face in thedirection of flow, whereby the pipes or pressure tubes'i'or conducting aportion of the flow down through the meter. The two pipes are perferablyarranged back to back so that they can be inserted through a. relativelysmall aperture III in the wall of aduct D; The lower ends of the twopipes are spread apart, as illustrated nd these ends have taperedextremities 98" and 99" for effecting tight seating in the upwardlydirected tapered ends of the two passageways I02 and I03. A circularcollar I is secured fast to the separated lower portions of the twopipes and is adapted to iit within a circular,

threaded boss I" which is secured to the top of the. meter housing. Aclamping nut I" is arranged to screw down over the boss I05, this nuthaving an inwardly extending flange which overlies the edge of thecollar I. It will be'evident that by screwing this nut I" downwardly,the

tapered extremities of the two pipes can be forced into tight seatingcontact with the tapered ends of 70 the passageways I02, I03. When thepipe attach-' ment 81 is disconnected from the instrument, the upperends of these passageways are closedby I a closure attachment I08,illustrated in Figure 14. The latter comprises two solid plugs I and 7sl l I extending down from a block I lland adapted to seat in the upperends oi the passageways I02, I N13 for closing the same. A screw cap H3has swiveled connection with the block H2 through 5 the swivel pin ill,whereby the screw cap can be screwed downwardly over the threaded bossI05 for forcing the plugs illil, Ill down into the passageways. when aninstrument of the construction illustrated in Figures 12 and 13 isprovided with a top carrying strap 5, one end of the strap is madereleasable to facilit te connecting the attachment 91 to the instrum t.

The two passageways I02, III! are formed within the mounting block 21and communicate with 15 the inlet and outlet ends respectively 0! theair channel. The adjustable top wall 38 oi the air channel is preferablyarranged so that these passageways open into the channel beyond the endsof said adjustable top wall. When thus employing the instrument inconjunction with the attachment 91 for measuring the velocity of a flowwithin a closed conduit, it is desirable that, the outlet apertures 31,31', 31" in the righthand side of the casing be closed. This isaccomplished by the provision of a shutter 'plate Ht which is arrangedfor sliding movement insideof the righthand casing wall 231',corresponding substantially to the slidable arrangement of-the shutterplate 85 at'the opposite side of the casing. For example, the plate Himay be provided with laterally extending marginal flanges Ilia whichcooperate with spring rods lll tor guiding the motion of the plate,similarly to the guiding relation previousiy described between theflanges 85a and the spring rods IS. The plate H6 is provided with threerows of relatively large apertures lilwhich are adapted to register withthe three rows of casing apertures l1, I1, 31" when the plate is in itslower position. The movement oi the plate to its upper position closesall rows 0! casing apertures. Such movement is eflected by an arm IIIwhich extends across the casing adjacent to the bottom thereof, Theleithand end of this arm isrigidiy secured to the lowerportion of theshutter slide 85 so as to move directly therewith. The arm is disposedadjacent to the back wall of the casing, as shown in Figures 5 and 6, sothat it can have the required range of movement in a plane in back ofthe permanent magnet N. The righthand and 01 said arm isadapted toengage w a flange I lib which is punched laterally from the lowerportion of the shutter plate H8. One or more tension springs I21,connected between the flanges l Ito and the bottom wall portion 48c,nornially tend to pull the shutter slide H6 down to its open position;The arrangement is such that the latter slide will remain in this (openposition, with theoutlet apertures, 31, 81', ll" completely open, aslong as the inlet shutter 85 is either down in itswide open position orin its intermediate restricted position with the resti'ic ted apertures93, 83 in register with the apertures.

However, as soon as theinlet opening'shutter 85 V is moved upwardly toits completely closed posi- ,;tlon, the corresponding upward movement ofthe 51m in will eil'ect engagement with the flange i Ito and move theoutlet shutter 8 up to its closed position, thereby closing both sidesof the casing. As soon as the inlet shutter is mpved back to itsintermediate position or to its lower position, the springs in restorethe outlet shutter m to its open position. Thus, the two shutters arecapable of completely closing the instrument housing, Wvhieh isparticuiar-1y desirable when the instrument is to 'struction-adapted forthe. use of the attachment have the attachment 9! adapted thereto formeasuring the velocity of a flowthroug'h a closed conduit, asillustrated in Figure 12. Even where the instrument is not intended ordesigned for this latter adaptability, the closing of the outlet 5apertures 31, 3.1, 31", when the instrument is locked against operation,is 01 advantage for preventing any possibility of the vane 35 beingsubjected to any air pressure. In the modified con- 10 81, the lockingwire 83 may be dispensed with so that the moving system is still movablewith both shutter slides elevated to their closed positions; or thislocking wire is retained by giving each of 1 the slides still anotherhigher ,position, beyond the closed positions, in which higher positionthe casing will still be closed and the wire will be brought into actionfor locking and elevating the moving system. It will be noted that whenthe conduit attachment 91 is coupled to the meter casing it constitutesa self-supporting extension from the casing whereby the casing can beemployed as a supporting handle for maneuvering the orifice end of theconduit into diilerent positions in the air stream. Also, the use of theextension conduit is advantageous in situations where the presence oi!the meter casing directly in the air stream would cause such turbulenceand blocking effects in the air flow as to result in erroneous readings,the relatively small size or the extension conduit not causing suchobiectionable turbulence or blocking eilect.

I have found that the magnetic damping mechanism, constructed andarranged substantially as herein described, is ei'llcacious to dampen.the motion of the moving system when low velocity air currents areadmitted through the unrestricted apertures 36, 36' or when therestrictedapertures 93, 93' are interposed for higher velocity currents.The eddy currents that are set up in the damping segment 5! upon anytendency of the segment to oscillate quickly, oppose sufllcientretarding force to such quick motion that a dead beat indication isobtained even when the air velocities are rapidly pulsating. In the caseof a rapidly pulsating air flow, the indication is substantially themean 01" the diflerent velocities. This magnetic damping operationcreates noririctional retardation and does not decrease the sensitivityof the instrument. Also, this magnetic damping operation if enables theindicating pointer to follow such slow surges or changes in velocity ascan be read directly without inconvenience, which is often desirableFurthermore, such magnetic damping also damps the indicating-meansagainst any 5-5 vibration or motion which may arise from holding themeter in the hand during the taking oi' velocity measurements. i

. While I have illustrated and described what I regard to be thepreferred embodiment of my 00 invention, nevertheless it will beunderstood that such is merely exemplary and that numerous modificationsand-rearrangements may be made therein without departing from theessence oi the invention. 7

I claim:-- s

1. In an air yelocity meter of the class described, the combination of acasing, 6 air channel defined in said casing for directing an airflowtherethrough, a moving system comprising a vane, indicating means and abalancing segment, .said vane extending into said air channel inposition to be deflected through a limited range of oscillatory movementby the velocity of the air flow through said channel, said indicatingmeans indicating the stantially at right angles thereto and balancingsaid vane and indicating means, and a permanent magnet comprisin poleextremities defining an air gap, said balancing segment moving throughsaid air gap.

2. In a portable air velocity meter 01 the class I described, thecombination of a casing, inlet and outlet openings in opposite sidewalls of said casing, an air channel in said casing extending in asubstantially straight. line between said openings, whereby saidopenings can be aligned with free atmospheric, air currents and saidcurrents can have substantially unidirectional flow throughsaid casing,a moving system comprising a vane, indicating means and a balancingsegment, said vane extending into said air channel in position to bedeflected through a limited range of oscillatory, movement by thevelocity of the air flow through said channel, said indicating meansindicating the range of deflection. of said vane, said balancing segmentdepending below said vane and lying substantially at, right anglesthereto and substantially balancing said vane and indicating means, anda permanent magnet comprising pole extremities defining an air gap, saidbalancing segment moving through said air gap.

3. In a portable air velocity meter of the class described, thecombination of a casing, inlet and outlet openings in opposite sidewalls of said casing, an air channel in said casing extending in asubstantially-straight line between said openings, whereby said openingscan be aligned with free atmospheric air currents and said currents canhave substantially unidirectional flow through said casing, a movingsystem comprising a vane, indicating means and a damping segment, saidmoving system being pivoted for, oscillatory movement about an, axisextending substantially at right angles to the direction of flow' of theair through said, channel, said vane extending into said channel andbeing disposed substantially transversely thereof in position to bedeflected through a limited range of oscillatory movement by thevelocity of the air flow through said chan-- nel, said indicating meansindicating the range of deflection of said vane, said damping segmentdepending below said vane and lying substantially at right anglesthereto, and permanent magnet means comprising pole extremities definingan air gap, said damping segment moving through said air gap.

4. In a portable air velocity meter of the class described, thecombination of a substantially rectangular casing which can be held inthe hand or rested on a supporting surface for operation, inlet andoutlet openings in opposite side wallso! the upper portion of saidcasing, an approximately horizontal air channel in the upper portion ofsaid casing extending in a substantially straight line between saidopenings, whereby said openings can be aligned with free atmospheric aircurrents and said currents can have substantially unidirectional flowthrough Said casing, a spindle in said casing below said air channel andextending substantially at right angles to the direction of flow of theair through-said channel, a U-shaped permanent magnet disposedsubstantially horizon-.

tally in said casing belowsaid spindle, and a moving system comprising avane, indicating means.

and a balancing segment pivotally mounted on said spindle, said vaneextending into said channel and being disposed substantiallytransversely .thereof and closing the major portion of said channel whenin "zero position, said indicating a means indicating the range ofdeflection of said vane, said balancing segment depending below. saidvane and lying substantially at right angles thereto and moving betweenthe pole extremities of said permanent magnet.

5. In a portable air velocity meter of the class described, thecombination of a casing, an air channel defined in said casing fordirecting an air flow therethrough, means for controlling the air flowthrough said channel, a moving system commeans, and a permanent magnetcomprising pole extremities defining an air gap, said balancing segmentmoving through said air gap.

6. In a portable air velocity meter of.,the class described, thecombination of a casing, inlet and outlet openings in said casing, anair channel in said casing extending between said openings, adjustablemeans actuatable from the exterior of said "casing for controlling theefiective area of one ofsaid openings to adapt the meter to differentranges of velocities, a moving system comprising a vane and indicatingmeans, said moving system being pivotedfor oscillatory move ment aboutan axis extending substantially at right angles to the direction of flowof the air through said channel, said vane extending into said channeland being disposed substantially transversely thereof and closing themajor portion of said channel when in zero position, said indicatingmeans indicating the range ofdeflection of said vane, said indicatingmeans having multiple scale means cooperating therewith for described,the combination of a casing, an air channel defined in said casing fordirecting an air flow therethrough, adjustable means controlling the airflow through said channel foradapting the meter to different ranges ofvelocities, a moving system in said casing comprising a vane andindicating means, said vane having osc1l-- latory movement in said airchannelabout a. pivot axis extending substantially at right angles tothe direction of flow of the air through said channel, said indicatingmeans indicating the range of deflection of said vane and comprisingmultiple scale means forgiving different readings for different rangesof velocities, a designating device operating in conjunction with saidadjustable controlling means for designating the scale of said multiplescale means to be read, and magnetic means for damping the motion ofsaid moving system.

ings, whereby said openings can be aligned with freeatmospheric-aircurrents. for substantially unidirectionalflow through said casing, amoving system comprising a pivoted vane, indicating means and a dampingmember on'opposite sides of the pivot axis of the vane, said vaneextending into. said air channel in position to be deflected through alimited range of oscillatory movement by the velocity of the air fiowthrough said channel and the general axis of said channel being.

spaced to one side of the pivot axis oi said vane, said indicating meansindicating the range 01 deflection of said vane, permanent magnet meanscomprising pole extremities defining an air gap and disposed on the sideof said pivot axis opposite side air channel, said damping member movingthrough said air gap,-a hair spring opposing motion of said movingsystem in one direction, and means for adjusting the zero position ofsaid indicating means through said hair spring;

9. In a portableair velocity meter of the class described, thecombination/of a casing, an air channel defined in said casing fordirecting an air flow therethrough, a moving system in said casingcomprising a vane, indicating means and a damping member, said vanebeing disposed substantially transversely in said air channel and havingoscillatory movement therein about a pivot axis extending substantiallyat right angles to the direction of flow of the air through saidchannel, said indicating means indicating the range of deflection ofsaid vane, a hair spring for restoring said moving system to zeroposition, and permanent magnet means in said casing comprising poleextremities defining an air gap,

said damping member moving through said air gap and being constructed toexert diiIerent degrees oimagnetic retardation to motion of sal d,moving system in difierent angular positions of said moving system,whereby said ,damping member exerts minimum magnetic retardation whensaid moving system is in close proximity to its zero position. g

10. In a. portable air velocity meter of the class described, thecombination of a casing, an air channel definedin said] casing fordirecting an air fiow therethrough, a moving system comprising a vaneand indicating means, said moving system being pivoted for oscillatorymovement about an axis extending substantially at right angles to thedirection of flow of the air through said channel, said vane extendinginto said channel and being disposed substantially transversely thereof,said indicating means indicating the angular deflection of said vane,mag- 'netic means for damping the motion of said moving system,including a partxmovable with said vane, and locking means for holdingthe moving system against motion comprising a member movable intoengagement with the movable part of said magnetic damping means,

11. Infan airvelocity meter of the class de-'- scribed, the combinationof a casing, an air channel defined in said casing for directing an airflow therethrough, a moving system'comprising a vane, indicating means:and a balancing segment, said vane extending into said air'channel andpositioned tobe deflected through aiimited range of'oscillatory movementby'the velocity of the air now through said channel, said indicatingmeans indicating the range or deflection of said vane, said balancingsegment depending below said vane and lying substantially at rightangles thereto and substantially'balancing said vane and indicatingmeans, apermanentmagnet comprising pole extremities defining an air g'apsaid balancing segment moving through said air gap, and a movable walldefining a part of said air channel movable to different positions forchanging one of the dimensions oi said channel.

. 12. In a portable 'air velocity meter of the class described, thecombination of acasing, an air channel defined in said casing fordirecting an air flow therethrough, a moving system in said casingcomprising a vane, indicating means and a balancing segment, said vaneextending into said air channel in position to be deflected through alimited range or oscillatory movement by the velocity of the air flo'wthrough said channel, said channelvarying in cross-sectional areabetween different points of its length, ,whereby said vane in a lowvelocity'position closes a greater proportion of said channel than itdoes in a high velocity position, said indicating means indicating therange of deflection of said vane, said valancing segmentdepending belowsaid vane and lying substantially at right angles thereto andsubstantially balancing said vane and indicating means, and a permanentmagnet in said casing comprising pole extremities defin-v moving ancingsegment, said moving system being pivcited for oscillatory movementabout an axis extending substantially at rightangles to the direction offlow oi the air through said channel,

said vane extending into said channel and being disposed substantiallytransversely thereof and closingthe major portion of said channel in allpositions thereof, said air channel varying incross-sectional areabetween different points of its length, whereby said vane closes agreater proportion 01 the channel-in a low velocity position than itdoes in a high velocity position, said indicating means indicating therange of de-- fiection of said vane, said balancing segment dependingbelow said vane and lying substantially at right angles thereto and.substantially balancing said vane and indicating means, and a permanentmagnet in, said casing comprising pole extremities defining an air gap,said balancing segment moving through said air; gap.

14. In a portable air velocity meter of the class described, the.combination of a casing, inlet and outlet openings in opposite sidewalls of said cats-- ing, an air channel in saidcasing extending in asubstantially straight line between said openings, whereby said-openingscan be aligned with free atmospheric air currents and said currentscan.

havesubstantlally uni-directional flow through said casing, av nepivoted for oscillatory movement about ain'axis extendingsubstantially-at right angles to thedirection of flow of the air throughsaid channel, said vane being disposed substantially transversely insaidchannel and closing approximatelrthe entire cross-sectio area oi saidchannel when in its zero position,v

said vane 61051118112118 maior-cross1sectional area 01' said channel inall posltions thereof; said channel increasing in cross-sectional areato-' wards the position 0! maximum deflection of said vane, indicatingmeans indicating the angular deflection of said ,vane and comprisingdiflerent 'scale dataior diflerent ranges of velocities, ad-

Justable means for controlling the eil'ective area of one of saidopenings to adapt the meter to diflerent ranges of velocities, anddesignating -means operating therewith for designating the ing, an airchannel in said casing extending in a conduit.

substantially straight'line between said openings, whereby said openingscan be aligned with free atmospheric aircurrents and said currents canhave substantially uni-directional flow through said casing, a vanepivoted for oscillatory movement about an axis extending substantiallyat right angles to the direction of flow of the air through saidchannel, said vane being disposed substantially transversely in saidchannel and closing approximately the entire cross-sectional area ofsaid channel when in its zero position, said vane closing the majorcross-sectional area of said channel in all positions thereof, saidchannel increasing in cross-sectional area towards the position ofmaximum deflection of said vane, indicating means indicating the angulardeflection of said vane, a conduit for adapting the meter to themeasurement of fluid flow at a point removed from the meter, saidconduit having anorifice at one end adapted to be inserted into theregion of flow to be measured, detachable coupling means for couplingthe other end of said conduit to said casing, the latter end of saidconduit; communicating with the inlet end of said channel when socoupled to the meter, and means for closing theremainderof the inlet endof said channel from communication with atmosphere when the meter isthus adapted to the measurement of flow conditions through saiddetachable 16. In a portable air velocity, meter ofthe class described,the combination of a casing, inlet and outlet openings in opposite sidewalls of said casing, an air channel in said casing-extending in asubstantially straight line between said openings,

whereby said openingscan be aligned with free atmospheric air currentsand said currents can have substantially uni-directional flow throughsaid casing, a vane'pivoted Ior oscillatory movement about anaxisextendi'ng substantially at right angles to the direction of flow oithe air through said. channel, said vane being disposed substantiallytransversely in said channel and closing approximately the'entirecrossrsectional area 01' said channel when in its zero position, saidvane closing the major cross-sectional area oi said channel in allpositions thereof, said channel increasing in stress-sectional areatowards the position'of maximum deflectioh of said vane, indicatingmeans indicating the angular de-- ilection oi said vane, adjustablemeans actuatable from the exterior of said casing for controlling theeffective area 01 one of said openings to adapt the meter to differentranges of velocities, a con-- duit i'or adapting the meter to themeasurement oLfluid now at a point removed from the meter, said conduithaving, an orifice at one end adapted to be inserted into the region offlow to be measatmosphere when the meter is thus adapted to themeasurement of flowconditions through said detachable conduit. I

17. In a portable air velocity meter of the class described, thecombination of a casing an air channel in said casing for directingan,a.ir flow therethrough, a vane disposed substantially transversely insaid channel and having limited oscillatory movement thereinabout apivot axis extending substantially at right angles to that portion ofthe channel through which said vane swings, said'vane in itszeroposition being inclined from the vertical and closing approximatelythe entire cross-sectional area or said channel, said vane closing themajor crosssectional area of'said channel in all positions,

, said channel increasing in cross-sectional area towards the positionof maximum deflection o1 said vane, indicating means indicating theangular deflection of said vane, magnetic means for damping the motionof said indicating means,

an extension conduit, means for detachably coupling one end of saidconduit to said casing in communication with the inlet end of saidchannel, the other end of said conduit having an orifice therein forconducting exploring operations in velocity regions remote from saidmeter,

and means for closing the remainder of the inlet portion of said channelfrom communication with atmosphere when the meter is thus used for theto be deflected through a limited range of oscillatory movement bythevelocity of the airy flow through said channel, said indicating meansindicating the range of deflection of said vane, said balancing segmentdepending below both said vane and said air channel and lyingsubstantially at rightanglesthereto and substantially balancing saidvane and indicating means, and a' permanent magnet comprising poleextremities defining an air gap, said'balancing segment moving throughsaid air gap.

19.'.In a portable air velocitymeter of the class described, thecombination of a casing, inlet and outlet openings in opposite sidewalls of said casing, an air-channel in said casing extending in asubstantially straight line between said openings, whereby said openingscan be aligned with i'ree atmospheric air currents and said currents canhave substantially uni-direetional'flow through said a moving system insaid casing comprising a vane and indicating means, and means foradapting the meter to the measurement or fluid flow within a closed ductor the like comprising a'conduit adapted'to have communication at oneend with the inlet portion of said air chan- Y nel and having its otherend adapted to open into 7 said duct, and means for closing the inlet'open ing 01 said casing from communication with atmosphere when themeter is thus adapted to the measurement thelike. i

20. In a portable air velocity meter of the class described, thecombination of a casing, an air channel extending in a substantiallystraight line through said casing, whereby said channel can be alignedwith free atmospheric air currents and said currents can have.substantially r fluid fiow within a closed duct or 1 tlonal flow throughsaid casing, a vane in said charmel pivoted i'or oscillatory movementabout an axis extending substantially at right angles to the direction01 flow of' the air through said 5 channel, indicatingmeans indicatingthe angular deflection oi-said vane, said vane responding to freeatmospheric air currents of relatively low velocity passing through saidchannel, ex-r tension means for adapting the meter to the 10 measurementof fluid flow within a closed duct or in othervelocity regions removedJrom the meter, comprising two conduits communicating with opposite endsoi! said channel. the other'ends of said conduit-shaving orificestherein adapted g to be presented in diflerent angular relationsto thefluid flow in the velocity region being measured, and means for closingthe inlet and outlet ends of said channel from communication withatmosphere when the meter is thus adapted to go the measurement of fluidflow through said extengg of said casing, an air. channel in said casingsion means.

21. In a portable air velocity meter of theclass described, thecombination 01' a casing, inlet and outlet openings in opposite sidewalls extending in a substantially straight line he: tween saidopenings, whereby said openings can be aligned with tree atmospheric aircurrents and said currents can have substantiallyuni- I so directionalflow through said casing, a moving system in said casing comprising avane and indicating means, means for adapting the meter to themeasurement 0! fluid flow with a closed duct or the like comprising aconduit adapted 35 to havecommunication at one end with the inletportion of said air channel and having its other end adapted toopen'into said duct, and means carried by the casing for closing theinlet open-- ing of said casing from communication with 0 atmospherewhen the meter isthus adaptedto the measurement of fluid flow within aclosed duct or the like.

22. In a portable air velocity meter oi the class described, thecombination 0! a casing, I 45 inlet and outlet openings in opposite sidewalls of said casing, an air channel in said casing .extending in a'substantially straight line between said .openings, whereby saidopenings can be aligned with i'reeatmosphericair currents and go saidcurrents can have substantially unidirecment of fluid tional flowthrough said casing, a moving system in said casing comprising a vaneand indicating means, means for adapting the meter to the" measurementof fluid flow within a closed duct .55 or the like comprising a conduitadapted to have communication at one end with the inlet portion of saidair channel and having its other end adapted to open into said duct. andmeans carried by the casing against'said opposite side walls forclosingboth said inlet and outlet openings oi the casing tromcommunication with atmosphere when the meter isthus adapted to themeasureflow within a closed duct or the 23. In a portable air velocitymeter of the class described, the combination oi a casing,

inlet and outlet openings in opposite side walls of 1811113881215!!! airchannel inisald casing extending in a substantially straight linebetween said openings, whereby said openings can be aligned with treeatmospheric air currents and said currents can havesubstantially-unidirectionai new through'said casing, means carried bythe casing and serving as a-lower wall for the inlet 1 portion or saidair channel, amoving system in said casing comprising a vane andindicating means pivoted for movement about an axis spaced below saidwall means, and a curved partcarried by said vane and arcuate about saidaxis so as to cooperate with said wall means so as to restrict airleakage from he inlet portion or said air channel.

24. In a portable air' velocity meter of the class described, thecombination of a casing, inlet arid outlet openings in opposite. sidewalls of said casing, an air channel in said casing extending in asubstantially straight line between said openings, whereby said openingscan be aligned with tree atmospheric air currents and said currents canhave: substantially unidirectional flow through said casing, meansserving as a lower wall 'ior the inlet portion of said air channel, amoving system in'said casing comprising a'vane and indicating meanspivoted for swinging movement about an axis below said wall means, saidvane including a substantially flat section closing approximately theentire cross-sectional area of said air channel and-having a laterallybent sec-r tion with a portion curved arcuately about said pivot axisand cooperating with the inner end 01' said wall means in all positionsof the vane for the purpose of preventing air leakage at this point, andbalancing means for (said vane.

25. In an air velocity meter oi the class described, the combination ofa casing, an air ing said vane and indicating means, means ior closingthe ends of said air channel, and means operable therewith and movableinto and out of engagement with said balancing segment for holding themoving system against, motion.

26. In an air-velocity meter of the class de -f scribed, the combinationoi a casing, an air cha neldeflnedin the upper portion of said casingfor directingan air flow therethrough, a

moving system comprising a vane, indicating means and a balancingsegment, said vaneextending into said air 'channel "and positioned to bedeflected through a limited range oi'oscillatory movement ,by thevelocity of the air flow.

through said channehsaid indicating means indicating the range ofdeflection or said vane, said balancing segment depending below saidmile and lying substantially at right angles thereto and substantiallybalancing said vane and indicatlng means, shutter means for closing theinlet end of said air channel and including a portion extending intothelower part of said casing, and a locking, member in the lower portionof said casing and movable into elfgagement with said balancing segment,said locking mber being operatively connected with the lower portion ofsaid shutter i 27. In a portable air velocity meter of the classdescribed, the combination oi a 'casingyall 31;- channel in said casingincreasing in area towards its outlet end, a moving 'systemcomprising avane closing-the niaior portion of said channel and movablejbout a Pivotaxis disposed substantially at right angles to the channel fordeflection by the air now therethrough, a spring opposing such motion ofthe vane, an indicating device associated with said moving-system forgiving direct readings in terms of air velocity from the deflection ofsaid moving 'system, inlet and outlet means comprising apertures inopposite side walls of said casing and the air channel being disposed soas to extend in a substantially straight line between said apertureswhereby the latter can be aligned with free atmospheric air currents anda substantially uni-directional air flow provided through the meter,said inlet and outlet means being of relatively large efiective area forrendering said meter responsive to relatively feeble air currents, anextension conduit attachment comprising a stem portion having orificemeans at the outer end thereof for introduction into a closed .duct orother region of air flow removed from the meter and adapted to have itsother end placed in communication with said air channel, said stemportion being of substantially uniform cross ,section throughout itslength for movement through a relatively small aperture in the wall ofsaid duct and comprising two passageways,

one leading from the region of air flow to the T deflection by theairflow therethrough, a spring opposing such motion of the vane, anindicating inlet end of said air channel and the other leading from theoutlet end of said air'channel back to said region of air flow, wherebysaid air channel may be selectively placed in communication through saidinlet and outlet means directly with 'fre'e atmospheric air currents inwhichthe meter itself is situated or through said extension con 'duitwith an air flow at a point removed from the meter, and means forpreventing free atmospheric air currents in which the meter itself maybe, situated from passing through said air channel when said extensionconduit is placed in communication with the meter.-

' 28. In a portable air velocity meter of the class described, thecombination of a casing, an air channel in said casing, afmoving systemcomprising a vane movable in said air channel for device associated withsaid moving system for giving direct readings in terms of air velocityfrom the deflection of said moving system, inlet and outlet means insaid casing for passing air through said channel from the immediateexternal vicinity of said meter, an extension conduit attachment havingorifice means at one end for introduction into a,closed duct or otherre-, vgion-ofair flow removed from the meter and adapted to have itsother end placed in communication with said, air channel, said extensionconduit attachment comprising two ducts, one leading from the region or,air now to the inlet end of said air channel and the other leading irom'the outlet end oi said air channel back to said'region of air flow,whereby said air channel may be selectively placed in communicationthrough said extension conduit with an air flow 'at a point removed fromthe meter or through,

said inlet and outlet means directly with an air flow in which themeteritseli'is situated, and means for preventing an air flow in which themeter itself may'be situated from passing through said air channel whensaid extension conduit is,

placed in communication with the, meter.

29. In a portable air velocity-meter oi the class described, thecombination oi" a. casingfia'n'air 7 channel in said casing, a movingsystem compriiinrrvanembvable in said air channel for deflection by theair flow therethrongh, a spring which the meter itself may classdescribed, the. combination of opposing such motion of the vane, anindicating device associated with said moving system for giving directreadings in terms of air .velocity from the deflection of said movingsystem, inlet and outlet means comprising apertures in the opposite sidewalls of said casing and the air channel being disposed so as to extendin a sub-- stantially straight line between said apertures wherebythe'latter can be aligned with free atoutlet m eans directly with freeatmospheric air currents'in which the meter itself ,issituated orvthrough said extension conduit with an air flow at a point removed fromthe meter, and means for preventing free atmospheric air currents inwhich the meter itself may be situated from passing through said airchannel when said extension conduit is placed in communication with themeter.

30. In a portable air velocity meter of the class I described, thecombination of acasing, an air channel in said casing, a moving systemcomprising a vane movable in said air channel for deflection by the airflow there 'hrough, a spring opposing such'motion of the vane, anindicating device associated with said moving system for giving directreadings in terms of air velocity from the deflection of said movingsystem, inlet and outlet means in said casing for passing air throughsaid channel from ithe immediate external vicinity of said meter, anextension conduit attachment having; orifice means at one end forintroduction intog a closed duct or other region of air flow removedfrom the meter and adapted to have its other end placed in communicationwith said air channel, wherebysaid air channel may be'selectively placedin communication through said extension conduit with an air flow at apoint removed from the meter or through said inlet and, outlet meansdirectly with an air flow in which the meter itself is situated, andmeans for preventing an air flow in be situated from passingthroughsaidair channel when said extension conduit is placed'in communication withthe meter.

31. In a portable air velocity meter :of the a casing, an air channel insaid casing, a moving system comprising a vane movable in said air.c'hannel for deflection by the air-flow therethrough, a spring opposingsuch motion 01 the vanefmeans for substantially balancing said vane tomaintain the accuracy of the meterv when held at diiferent angles, anindicating device associated with said moving system for giving directreadings in terms of air velocity from the deflection of said moving sytem permanent magnet damping means for damping the motion ofsaidindicating device, an

extension conduit attachment having orifice means at one end forintroduction into a closed duct or other region' of air flow removedfrom thd meter, and coupling means for placing the other end of saidextension conduit in commuchannel may be selectively placed irr communi-Q nication with said air channel, whereby said air,-

air flow at a point removed from the meter or directly with anair flowin which the meter itself is situated.

moving system comprising a vane movable in saidair channel fordeflection by the air flow therethrough, a spring opposing suchmotion ofthe vane, said moving system being substantially .line between saidapertures whereby the latter can bealig-ned with free atmospheric aircurrents and a substantially uni-directional air flow provided throughthe meter, an extension conduit attachment having orifice means at oneend for introduction into a closed duct or other region of air flowremoved from the meter, and quick detachable coupling means for couplingthe other end of said extensionconduit in communication with said airchannel, whereby said air channel may be selectively placed incommunication through said inlet and outlet means directly withfree.atmospheric air currents in which the meter itself is situated orthrough said extension conduit with an air flow at a point removed fromthe meter. g 33. A portable air velocity meter of theclass describedcomprising a casing, an .air channel in said casing increasing incross-sectional area toward the outlet end thereof, a moving systemcomprising a vane movable in said air channel for deflection bythe airflow therethrough, a spring opposing such motion of the vane, anindicating device actuated by said moving system for giving directreadings in terms of air velocity from the deflection of said movingsystem, a substantially rigid conduit attachment comprising a stemportion having orifice means at its outer end for introduction into aclosed duct or other region of air flow removed from the meter andformed with two passageways communicating with said orifice means, andreleasable coupling means for detachably'coupling the other end of.

a said conduit attachmentto the meter casing with end of said stem,portion into different positions said two passageways communicating withopposite ends of said air channel, said conduitattach-z mentconstituting a substantially rigid seli-supporting extension ,whencoupled to said meter casing whereby said casing can function as a themeter is'operated in different angular positions, velocity indicatingmeans actuated by said moving system, and an extensionconduit havingorifice means at one end for introduction into a a self-supportingextension from the m'etercasf ing whereby said casing conjunction as asupporting handle for maneuvering the. orifice end of said extensionconduit into different positions in the air stream. I

35. A portable air velocity meter of the class described comprising acasing, an air channel in said casing, a moving system comprising a:vane movable in said air channel for deflection by the air flowtherethrough, said vane moving about an axis disposed substantially atright angles to the direction of flow of the air through said channel, aspring opposing the motion of said moving system, an indicating deviceassociated with said moving system for giving direct readings in termsof air velocity from the deflection of said moving system, inlet-andoutlet aperture means in opposite side walls of said casing for passingair through said channel, and a shutter member movably carried by saidcasing and actuatable' movable into predetermined relation to one of.said aperture means in the casing for reducing by 'a predeterminedextent the eflective area of said latter aperture means for adapting themeter to the measurement of a higher range of velocities. 36. In aportable air velocity meter capable of being held in the hand and ofbeing inclined at diflerent operating angles during use, thecombinationof a casing, an air channel insaid cas-' ing, a moving systemcomprising a vane movable in said air channel for deflection by the airnow 7 therethrough, spring means opposing such motion of the vane,indicating means adapted to give direct'readings in terms of ,airvelocity from the deflection of said moving system, a conduit having oneend connecting with said air channel and having orifice means at itsother end adapted for introduction into a closed duct or other region ofair flow relatively remote from said casing so that velocitymeasurements can be taken at points inaccessible to said casing and sothat inaccura cies arising from, the turbulence created by disposing thecasing in the air stream are avoided, means for substantially balancingsaid moving system to maintain the accuracy of the meter when held atdifferent angles, and damping means equally eflective in any position ofthe meter for damping said indicatingmeans, said balancing means andsaid damping means cooperating to maintain the accuracy of the meterwhendisposed in or moved to different angles orpositions as may berequired to secure the desired readings. 37; A portable air velocitymeter'comprising a casing, an air channel in said casing, inlet andoutlet apertures for said channel in opposite side swalls of said casingi'or'passing air substantially in adirect straight line through saidchannel from one side of the casing to the other side, said hannelincreasing in cross sectional area toward the outlet end thereof, amoving system comprising a vane movable in said air channel generallylongitudinally thereof for deflection by the air flow therethrough,means yieldingly opposing "such motion 01' the vane and operativetorestore the" latter to normal position after cessation of air flow,means fox-substantially balancingsaid moving system to maintain theaccuracy of the meter when held at different; angles and when movedduring the use thereof, said opposing nected to'said meter casing incommunication closed duct or other region of air flow removed meansbeing q eflective i i POB t Ori o from the meter and having its otherend conthe meter, an indicating device associated with with said airchannelfisaid conduit constituting terms of air velocity from thedeflection oi said said moving system for giving direct readings inmoving system, and damping means for damping the movements of saidmoving system, said damp ing means being equally efiective in'anyposition of the meter, the arrangement of the inlet and out-iet openingsin opposite side walls of the casing providing for movement of the metertransv rsely oi the air iiow be g measured Withc'ut

